This invention relates to a spray type retort sterilizer, and more particularly a spray type retort sterilizer which performs various kinds of high-pressure sterilization of gas foods containing a lot of gas, transfusion soft pack for medicine, etc. Conventionally, various kinds of device which performs pressurized heat sterilization by using either a steam type or a hot-water type retort have been put into practice as retort sterilizer. Such devices are described in the Japanese Bulletins of Publicized Patent No. 58-57146 and No. 58-57147, for example.
In the steam type retort sterilizer, the object material to be sterilized is placed in the retort by loading the material on trays and stacking these trays. The steam outlet is designed in most cases in such a way that the steam may be discharged from the bottom of the retort toward the top. As a result, it was often the case that the object material placed on the trays at the lower part is heated at a proper temperature while the object material placed on the trays at the top part remains in the state of uneven sterilization due to a drop of temperature of the steam as it rises through the retort.
Moreover, a hot-water type retort presented a problem in that the object material stored in the trays gets unstable under the influence of the buoyancy of the hot water, requiring a complicated construction having a presser lid for the trays. The influence of the buoyancy was particularly large in the case of gas foods, while a problem with transfusion soft pack for medicine, etc. is that the very act of submerging the material in hot water is undesirable.
This inventor proposed, in the Japanese Utility Model Gazettes No. 63-16519, No. 64-19436, No. 64-19437, No. 64-19438 and No. 64-20849, a retort sterilizer which, though of steam type, can solve the above problems and enable even sterilization of the object material in the trays with fine mist sprayed from spray nozzles provided on header pipes which are installed vertically or horizontally at positions close to the tray of each stage.
By the way, in the retort sterilizer already proposed by this inventor, etc., hot water is sprayed on the object material in hot water drops of a particle size of 0.2.about.0.6 mm or so (in the shape of sesame particle). In that case, hot water drops of a particle size of 100.degree. C. hot water sprayed from the nozzles instantly turn into steam by boiling and cannot be sprayed on the object material in the desired state of hot water drops if the internal pressure of the sealed retort is equal to the atmospheric pressure, for example. If you increase the size of the hot water drops, for example, to prevent such boiling phenomenon, those hot water drops cannot be sprayed to distant points. On the contrary, if you increase the spraying force to make the hot water drops go further, it leads to either breaking of the plastic pack containing the object material i.e. the material to be sterilized or deformation of the pack. Namely, the above-mentioned problem is produced as a result of softening of the plastic pack itself with the heat inside the retort.
This invention has been proposed, therefore, in view of the above problem and its object is to provide a retort sterilizer which does not produce any atomization by boiling in the retort even if the particle size of the hot water drops is 0.2.about.0.6 mm and the hot water temperature is 90.degree..about.130.degree. C.